In many environments, it is desirable to electroplate chromium onto cobalt-based alloy. One such application is the nose shields on induced draft fans operating in coal fired power plants. As such fans are often subjected to excessive fly-ash erosion, the economic loss due to plant shut-downs because of frequent fan blade protective shield replacements is high, and performance of the fans with regard to erosion is often unsatisfactory. While a nose shield of Haynes alloy 25 (approximately 10% nickel, 20% chrome, 15% tungsten, 3% iron, 0.1% carbon, 1% silicon, 1.5% manganese, 0.03% phosphorus, 0.03% sulfur and the balance essentially cobalt) plated with 30 mils of hard chromium was most promising from an erosion standpoint, the adhesion of chromium plate by any conventional plating processes was unsatisfactory and significant flaking resulted.
Heavy chromium deposits used in industrial or hard chrome plating applications such as this require essentially perfect adhesion to the base metal. Good adhesion of plating to carbon steel requires activation by reverse etching in the chrome plating solution. Stainless steels (18/8 type) require mechanical cleaning and activation in a fluoride or chloride solution prior to chrome plating. Conventionally refractory alloys such as Haynes alloy 25 have been treated with HCl, sulfuric acid or nitric acid prior to chrome plating, but poor adhesion has resulted.